1. Field of the Invention
The present invention relates to a linear motor, or more in particular, to a linear motor in which the ratio of teeth between the rotor and stator is fixed thereby to reduce the thrust pulsation for driving the rotor, thus making proper operation possible.
2. Description of the Prior Art
Conventional rotary-type motors, for example, have teeth of the magnetic poles thereof constructed as disclosed in the specification of French Pat. No. 1452379. In such a construction, the protrusions and the recesses of the stator are arranged equidistantly, and each protrusion of the rotor teeth has the same length as the stator protrusion while the rotor recess is one half of the protrusion thereof in length. For moving the rotor, therefore, at least four rotor teeth (protrusions) are required.
With an increase in the number of teeth, the frequency increases twice for the motors having the protrusions of the same pitch, resulting in an increased switching loss for control and increased noises.
In the presence of a thrust pulsation of this type of linear motor having teeth in the stator and rotor, the controllability is greatly deteriorated for achieving a predetermined speed or positioning as well as for speed control.
The thrust generated in the motor is determined by an induced voltage and the pattern and phase of the current supplied. The current pattern supplied has so far not been developed. In the linear induction motors, for example, the source voltage is applied directly, and there has been no cases describing the patterns of the current supplied.
On the other hand, a linear motor having a position detecting device is disclosed in Japanese Patent Unexamined Publication No. 166874/82. This linear motor comprises a rotary pulse generator mounted on the rotor thereof in order to detect the position of the rotor or the speed thereof. As a result, the wiring from the rotor is connected to a control circuit, thus giving no consideration to the movement over a long distance. In the encoder of contact type, by contrast, any attention is not paid to the high-speed movement either.